1. Field of the Invention
The present invention relates to a memory system including memory device and a memory controller via which the memory device is accessed.
2. Description of the Related Art
A microcontroller such as a CPU comes to have higher performance year by year. In accordance therewith, memory devices accessed by the microcontrollers and memory controllers need to have higher performance. Specifically, transfer rates (band widths) of data signals and so on between the microcontrollers and the memory devices have to be improved. In order to improve the transfer rate, in a certain kind of memory device, the number of bits in data signals is increased. Another memory device implements an interface circuit transferring serial data signals by using a high-frequency clock. Further, currently being considered are interface circuits transferring data signals each consisting of a plurality of bits, by using high-frequency clocks.
Interface circuits of conventional memory devices use electrical signals. The upper limit transfer rate of the electrical signals is said to be about 10 Gbps, and when it requires transfer rates higher than this, new interface circuits using optical signals and the like have to be considered.
For example, an art in which an optical interface is adopted between a microcontroller and a memory controller has been proposed (see, for example, Japanese Unexamined Patent Application Publication No. 2005-64950).
The Japanese Unexamined Patent Application Publication No. 2005-64950, however, does not describe details of the interface between the memory controller and memory devices. That is, it does not disclose the technology for improving transfer rates of signals transferred between the memory controllers and the memory devices.